Explain the process of the treatment of water at wastewater treatment plant (WWTP).

Discussion in 'CBSE Class 7 Science Help' started by g mahesh, Nov 11, 2013.

  1. g mahesh

    g mahesh Member

    Treatment of water involves physical, chemical and biological processes.

    (i) Wastewater is passed through bar screens which is used to remove rags, sticks, cans, plastic packets, napkins etc.

    (ii) Water then goes to a grit and sand removal tank. The speed of waste, water is decreased to allow sand, grit and pebbles to settle down.

    (iii) The water is then allowed to settle in a large tank sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This collected waste is called sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water.

    (iv) The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. Biogas produced in this process can be used as fuel or can be used to produce electricity.

    Air is pumped into clarified water to help aerobic bacteria to grow, witch consume human wastes, food wastes, soaps and other unwanted matter still remaining in clarified water.

    After several hours the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top.

    The activated sludge contains about 97% water. Water is removed by sand drying beds or machines. Dried sludge is used as manure. The treated water has a very low level of organic material and suspended matter. It is discharged into a sea, a river or into the ground. Nature cleans it up further.

    Sometimes it may be necessary to disinfect water by mixing chemicals like chlorine and ozone before releasing it into the distribution system.

Share This Page